In recent years, study has been carried out on the so-called augmented reality (AR) by which various types of information are displayed superimposed on an image captured by a camera, in order to aid user work.
In a system that realizes augmented reality, it is important that virtual space be accurately aligned with real space in order to superimpose information on an appropriate position in an image captured by a camera. To this end, there has been proposed a technology for estimating the position and the orientation of a camera based on the position and the shape of a pre-placed known marker in an image (for example, see Kato et al., “An Augmented Reality System and its Calibration based on Marker Tracking”, Journal of the Virtual Reality Society of Japan, 4(4), pp. 607-616, December, 1999). Also, there has been proposed a technology in which two images showing a subject are captured from arbitrary two places, feature points are extracted from each of the images, and the three-dimensional coordinates of the corresponding feature points in the images are calculated using the principle of triangulation based on the coordinates of the feature points in each image (for example, see Yamada, et al., “Latest Algorithm of 3-D Reconstruction from Two Views”, a technical report from Information Processing Society, vol. 2009-CVIM-168-15, pp. 1-8, 2009).
However, there are cases in which it is difficult to accurately detect the marker in an image, depending on photography conditions. There are also cases in which the marker goes out of the photography range of the camera, and consequently, the marker is not shown in an image. In such cases, it is difficult to estimate the orientation of the camera based on the marker. Accordingly, there has been proposed a technology in which when an estimation result of a camera pose representing the position and rotation of a camera in a world coordinate system of the camera is not obtained using a marker, the camera pose is estimated using a known point whose three-dimensional coordinates are known in the world coordinate system (for example, see Japanese Laid-open Patent Publication No. 2014-92984).